Fiber optic towed arrays are commonly constructed of a series of sensors interconnected along and within a common hose or casing. The sensors are typically comprised of buffered (with thin, approximately 40-50 micron thick plastic coating) optical fiber precision wound with adhesives on concentric, rigid tubes or mandrels. In some cases, the outer tubes are surrounded by rigid, perforated, cylindrical ‘cages’.
The mandrels upon which the fiber is wound are typically rigid with an air backing to allow sufficient compliance of the structure so that the fiber can respond to applied acoustic pressure signals, yet not collapse at operating water depths. Since the completed towed array must be reeled onto a drum for storage, it must be relatively flexible. This requirement for flexibility limits the length of the individual rigid mandrels to not more than a few inches, thus a flexible link between the hundreds of rigid mandrels is required. The optical sensing fiber must be wound over this flexible link as well. The fiber wound around the tubes is interconnected by buffered fiber that is wound along flexible cylindrical links between the mandrels. Winding the optical fiber at a very closely controlled tension and pitch, while at the same time applying adhesive, over rigid mandrels and flexible links requires expensive and precise manufacturing equipment.
Two significant problems are associated with the current state-of-the-art fiber optic towed arrays. They are expensive to produce due to the high level of manual labor needed to fabricate the sensors and assemble the arrays. They also suffer from reliability during handling operations. Failures of the optical fibers within the array are caused by fiber abrasion and microbending at rigid-flexible structure interfaces and by crushing when exposed to radial compression while wound on a handling reel.
What has been needed is rugged fiber optic towed array that can be easily and relatively inexpensively manufactured that provides excellent acoustic properties and offering increased protection to the fiber optic to prevent damage to the fiber optic during towing and spooling during deployment and recovery. The present invention satisfies these and other needs.